Vestibular System - Lecture 12 Flashcards
what is the vestibular system
internal system used to resolve conflict
maintenance of gaze stability
what does the vestibular system do
senses position of your head in space
generate compensatory movements of the body to prevent falls or loss of balance
what is the vestibular system able to detect
speed changes while driving, running, etc.
side to side movement
up/down movements
sensory conflict
exists b/w the 2 sensory structures
the eyes and the ears
what does motion sickness result from
conflict b/w the eyes and the ears
absence of movement
overview of the flow of vestibular info
sensory input –> CN8 –> central processor –> motor output
sensory input
vision
proprioception
somatosensory
peripheral vestibular system (labyrinth and otoliths)
central processor
vestibular nuclei
–> along with info from the cerebral cortex and cerebellum
motor output
VOR (vestibular ocular reflex)
VSR (vestibular spinal reflex - balance rxns)
peripheral vestibular system anatomy
size of a dime
3 semicircular canals
2 otolith organs in each ear
semicircular canals are sensitive to
angular velocity as the head turns and body rotation
what are the semicircular canals responsible for
compensatory eye movements required to maintain a stable gaze
VOR
VOR
vestibular ocular reflex
to maintain a stable gaze –> eye movement must occur in a direction equal and opposite to head rotation and with equal velocity
semicircular canal orientation
all canals are at 90 degree angles to each other
work in pairs
how do the canals work in pairs
anterior canal in one ear works with the posterior canal of the other ear
horizontal canals work together
what do the semicircular canals have connections to
extra ocular muscles
planes of the canals closely match the planes of extra ocular muscles
parts of the semicircular canals
ampulla
cupula
hair cells
ampulla
enlargement at the end of each semicircular canal
ampulla fxn
sensory organ of the canals
ampularis
small crest in each ampulla
cupula
gelatinous mass over the crista ampularis into which hair cells project
what occurs as the cupula bends
firing of the hair cells increases or decreases depending on the direction of deflection
hair cells
cells location on the crista ampularis
where do hair cells project
in the cupula
connect to the vestibular N (CN8)
endolymph
fluid that fills the cavities of the inner ear
high in K+ and low in Na+
perilymph
fluid that surround the endolymph
separated from the endolymph
high Na and low K+
similar to CSF
endolymphatic sac
keeps fluid at constant level
do endolymph and perilymph ever mix
not under normal circumstances
hair cells –> firing rate
there is a resting firing rate of the vestibular N
what happens if the hair cells are bent towards the side of movement
there is excitation
increase in the firing rate
what happens if the hair cells are bent in the opposite direction
inhibition
decrease in the firing rate
what is firing rate dependent on
intensity and direction of head movement
what maintains gaze on a target when the head is moved
VOR - vestibular ocular reflex
what do signals from the semicircular canals cause
the eyes to move in a direction equal and opposite to the head and with the same velocity
what is the VOR mediated by
a reflex pathway b/w the semicircular canals and the extra ocular muscles
abnormal VOR
inability to focus on objects when the head moves
nystagmus
involuntary movement of the eye
normally occurs when the head is moving or following a target
what does a nystagmus consist of
slow component –> when the eyes slip off a target
a fast phase –> the quick correction back
what is the nystagmus named after
the quick phase
if there is weakness on one side –> the slow component is the side of the problem
how is a nystagmus documented
(+) LBN
(+) RBN
otolith
utricle
saccule
fxn of otolith
detects linear acceleration
gravity
VSR - vestibular spinal reflex
VSR
responsible for postural adjustments needed to regain balance
otolith structure
macula
otoconia
macula
hair cells covered by gel
otoconia
calcium carbonate crystals located on the top of the gel layer that covers the macula
what make the otolith responsible to gravity
weight of the crystals
what occurs as the head moves –> otolith
otoconia fall to one side and cause the hair cells to fire
